The invention relates to a method for immobilizing material contaminated with heavy metal ions, said metal ions in a liquid environment being allowed to react with a metal-complexing agent with the formation of a metal-complex, the metal-complex formed being mixed, in the presence of water, with an inorganic, hydraulic binder comprising blast furnace slag cement, fly ash cement or a combination thereof to form a matrix having reductive properties in the form of a hard, rocklike material.